Risk of nitrate leaching from two soils amended with biosolids

High concentrations of N and P in biosolids are one of the strongest appeals for their agronomic use. However, it is essential to understand the fate of N in soils treated with biosolids for both plant nutrition and managing the environmental risk of NO^sub 3^^sup -^ -N leaching. This work aims to evaluate the risk of nitrate leaching from a sandy Podosol soil and from a clay Ferrosol soil, each one amended at the range 0.5-8.0 dry Mg/ha rates of freshly tertiary sewage sludge, composted sludge, limed sludge, heating-dried sludge and solar-irradiated sludge. Results showed that for similar biosolids application rates NO^sub 3^^sup -^ -N accumulated up to 3 times as much in the Ferrosol than in Podosol soil. However, there was a fixed 20% NO^sub 3^^sup -^ -N loss from the 20 cm amended-Ferrosol topsoil, whilst the N-nitrified expected to leach down from 20 cm amended-Podosol topsoil layer ranged from 42% to 76% of the accumulated NO^sub 3^^sup -^ -N, depending on the biosolid type. After all, NO^sub 3^^sup -^ -N expected to leach from Podosol soil ranged from 0.6 (heating-dried sludge) to 3.9 times (limed sludge) relative to Ferrosol soil at similar biosolid application rates. Nevertheless, the risk of NO^sub 3^^sup -^ -N groundwater contamination caused by biosolids applied at 0.5-8.0 dry Mg/ha rates could be considered very low.[PUBLICATION ABSTRACT]